Aluminum and silicon containing metal powder and method of producing workpieces therefrom



ALUMINUM AND SILICON CONTAINING METAL POWDER AND METHOD OF PRODUCING WORKPIECES THEREFROM V Giinter Wassermaun, 'Clausthal-Zellerfeld, and Richard Weber and Werner Hiibinger, Frankfurt Main, Germany, assignors to Metallgesellschaft Aktiengesellschaft, Frankfurt am Main, Germany No Drawing. Filed June 9, 1958, Ser. No. 740,558

Claims priority, application Germany Aug. 31, 1955 4 Claims. (Cl. 29-1825) I' The present invention relates to an improved powdered aluminum composition containing a certain amount of silicon which is particularly suited for the production of workpieces by powder metallurgical processes involving deep deforming operations.

Previously in the production of workpieces from aluminum powder, aluminum powders were used in which the aluminum was either in the form of flakes (flake aluminum powder) or the form of globules (globular atomized aluminum powder), In some instances small amounts of other powders, for example, up to about 5% of silicon powder, were admixed with the aluminum powder. Flake aluminum powder was used to a greater extent than the globular powder. For. the production of workpieces, such powders usually were first compacted to form compacts by hot or cold pressing of the powder with or without sintering and such compacts then subjected to a hot deformation operation, such as by extruding, rolling or forging. When flake aluminum powder was used as the starting material, such powder was usually provided with an aluminum oxide content ofat least 6% and a total lubricant content less than 0.3% and had a shaken weight of at least 0.7 g./cm. at least 50% of the flaky particles having a thickness less than 2 mu in their smallest dimension.

2,978,7fld Patented Apr. 11, rear and 15% and preferably the globular aluminum powder an oxide content of between land 13%. The aluminum powder can also contain a small quantity of lubricant or grease, but this'should not exceed 0.35%. It is to be understood, of course, that the aluminum powder and silicon employed according to, the invention need not be absolutely pure but can contain the usual impurities.

The aluminum silicon powder composition according to the invention can also contain up to 8% of graphite powder, lead and of intermetailic compounds of aluminum or magnesium, such as Al Fe, MgZn Mg Si, CuAl Fe Al and Cu Al. These additions can be desirable when the composition is to be employed in the production of workpieces having good sliding properties, such as, for example, bearings.

The aluminum silicon powder composition according to the invention can be employed to produce workpieces with the usual powder metallurgical processes. For example, the powder is first compacted at room temperature and at elevated temperatures up to 480 C. to form a compacted workpiece in which the powder is only compressed in the direction of the pressure. Such compacting can be carried out in the usual presses or also by rolling the powder in a rolling mill. The compacted powder workpiece then is SllbjCCtCCl to a deformation.

operation in which the metal is plastically deformed in the same sense as in the working of cast metal, for example, by extruding, forging or rolling. The kneading of the preformed compact during the plastic deformation operation increases the density of the workpieces and. improves their mechanical properties. The plastic deformation operation is carried out at elevated tempera- It is an object of the present invention to provide an improved aluminum powder composition especially adapted for the production of workpieces by powder metallurgical processes involving deformation operations such as forging, extruding and rolling operations on powdered metal compacts which cause plastic flow of the metal in the compacts.

The aluminum powder composition according to the invention contains 20 to 35% of silicon. This silicon can be in the form of silicon powder simply admixed ith the aluminum powder. On the other hand, the ili llicon can also be partially or completely alloyed with t e aluminum from which the aluminum powder is pro duced. The aluminum powder composition according to the invention can therefore be: a simple admixture of aluminum powder with silicon powder; a mixture of aluminum powder, aluminum silicon alloy powder and silicon powder; or an aluminum silicon alloy powder.

The aluminum component of the powdered composition according to the invention is present in the form of a mixture of flake and globular atomized aluminum powder, in a proportion of 25 to 75% of flake powder to 75 to 25% of globular powder.

The term flake aluminum powder is used herein not only to signify flaky powders in which the flakes have flat surfaces but also flaky powders in which the flakes have elliptical or lens-like shapes and in which the flakes have irregular edges and the surfaces have depressions therein.

The aluminum powder employed according to the invention may have an oxide content and preferably the flake aluminum powder has an oxide content between 7 tures between-about240 and 550, preferably between 430 and 470 C. If low melting additions, such as lead, are contained in the powdered composition, preferably temperatures are employed which are below the melting point of such additions but where the quantity of such additions is relatively small, higher temperatures can be employed which are still below the melting point of the main metallic component of the powdered starting mater1als. The workpieces produced by the plastic deformation operation can be processed to produce the desired finished workpiece, such as, for example, bearings, pistons, slide plates and the like, by further cutting or non-cutting shaping operations, such as, for example, turning, milling or forging.

When aluminum-silicon powder compositions according to the invention are compacted by rolling and the plastic deformation of the rolled compacts is also carried out by rolling, the plastic deformation is preferably carried out in several hot rolling steps and the material is heated to about 520 C. between the rolling steps. The strip of plate thus produced can then be further shaped as described above to produce the finished workpieces, such as bearings. 7

The workpieces produced from the aluminum-silicon powder composition according to the invention by the procedures described above are distinguished by their high silicon content and despite such high silicon content they can be produced withrelatively low working pressures Compacts of flake aluminum powders are more e a elongation increases with increase in globular aluminum powder in the starting powdered material.

The following examples will serve to illustrate several embodiments of the invention:

' Example 1 A mixture was prepared of 39% of globular aluminum powder, 39% of lenticular flake aluminum powder, 20% of silicon powder and 2% of graphite powder. The globular powder employed had a 6% oxide content and was of a grain size that 80% of itsparticles had a diameter less than 40 mu. The flaky aluminum powder had an oxide content of 8% and was of a grain size that 55% thereof passes through a sieve having a 40 mu mesh I width. The grain size of the silicon powder was 60 um and that of the graphite was 40 mu. The mixture was cold pressed at a pressure of 2 t./cm. to produce com pacts of a diameter of 72 mm. The compacts were heated for one hour at 440 C. and extruded in an extrusion press to form a rod having a U-shaped cross section. Sections of such rod were then cut off and hot drop'forged onto the concave surfaces of bearing shell halves. After finishing and polishing the bearing surface, the bearingswere ready for use.

Example 2 of silicon. The total mixture was cold pressed at a pressure of 2.2 t./cm. to produce compacts of a diameter of 220 mm. After preheating such compacts to 470 C.. they were extruded to rods 66 mm. in diameter. The pressure employed in the extrusion press was 6-7 t./cm.=.

'trusion press (recipient diameter=300 mm., recipient temperature==300 C.) and extruded over a mandrel to,

produce a tube having an outer diameter of 65 mm. and an inner diameter of 47 mm. (extrusion pressure 6.5 t./cm. The tube served as starting material for the production of bearings and was processed by turning.

Example 5 A powder mixture composedof of silicon powder, 3% of graphite powder and 5% of lead powder and the remainder of an aluminum powder mixture of 75 of globular aluminum powder and 25% of flake aluminum powder was prepared. The total mixture was heated to 200 C. and pressed to compacts 75 mm. in diameter at 4.5 t./cm. pressure. The compacts'were preheated to 300 C. and extruded in a 400 ton extrusion press to form a rod having a U-shaped cross-section corresponding to the bearings to be produced (extrusion pressure 5.5 t./cm. Sections of the U-shaped rod were cut off and drop forged to produce a half bearing. After finishing and polishing, thebearing surfaces they were ready for use.

Sections were cut off from the extruded rod and drop forged at 500 C. into pistons. The pistons thus obtained had a low coeflicient thermal expansion (between 20200 C.=l5.3 l0- C.), a good hardness at elevated temperatures (38 kg/mm. at 350 C.) and a good elongation (0.8%).

Example 3 A mixture of 60% by weight of globular aluminum powder and 40% of flake aluminum powder was prepared and thismixture was then admixed with silicon powder and graphite powder to provide a total mixture containing 35% of silicon and 4% of graphite. The resulting mixture was then cold rolled between two rollers to produce a strip 10 x 4 mm. The strip was preheated to 450 C. and hot rolled in four passes (roller temperature 80 C.), with intermediate heating to 450 C. between the passes to produce a strip with a 75% reduction in cross-section. Sections of the resulting strip were cut off and drop forged to produce bearing halves.

Example 4 A mixture of 30% silicon powder, 6% of a powder of an aluminum iron intermetallic compound (Al Fe) and 64% of a mixture of equal parts by weight of globular and flake aluminum powder was prepared. Compacts were prepared from this by cold pressing at 2.2 t./cm. pressure. The compacts were then preheated to 460 C. and placed in the recipient of a. 3500 ton ex- Example 6 A mixture of 60% of flake aluminum powder and, I

40% of a globular aluminum alloy powder (alloy comder was admixed with this mixture so that the total silicon content of thetotal mixture amounted to 30%.

This mixture was cold pressed into compacts of a diam- I eter of 300 mm. at a pressure of 2.2 t./cm. After preheating the compacts to 420 C., they were placed in the recipient of a 3500 ton extrusion press and extruded to,

a rod 80 mm. in diameter (extrusion pressure 5.5 t./crn. Sections were cut otf from the extruded rod and drop forged to produce pistons.

This is a continuation-in-part of copending application Serial No. 606,952, filed August 30, 1956;

We claim: A

1. An aluminum-silicon powder composition for powder metallurgy comprising a mixture of a flake aluminum powder and globular aluminum powder, the proportions of flake aluminum powder to globular aluminum powder being to 25% 25% to 75%, and containing 20-35% of silicon.

2. An aluminum powder composition according to claim 1 in which said silicon is present in said powder composition as silicon powder.

3. An aluminum powder composition according to claim 1 inwhich at least a portion of said silicon is present in said powder composition in the form of an alloy with the aluminum of at least one of said aluminum powders.

4. An aluminum powder composition according to claim 1 also containing up to 8% of a powdered material selected from the group consisting of graphite, lead, Al Fe, MgZn Mg Si, CuAl Fe Al and Cu Al.

References Cited in the file of this patent UNITED STATES PATENTS 2,809,891 Ennor et al. Oct. 15, 1957 

1. AN ALUMINUM-SILICON POWDER COMPOSITION FOR POWDER METALLURGY COMPRISING A MIXTURE OF A FLAKE ALUMINUM POWDER AND GLOBULAR ALUMINUM POWDER, THE PROPORTIONS OF FLAKE ALUMINUM POWDER TO GLOBULAR ALUMINUM POWDER BEING 75% TO 25% : 25% TO 75%, AND CONTAINING 20-35% OF SILICON. 